Electrical activity and calcium signaling have significant roles in directing neurotransmitter specification. Changes in electrical activity by natural visual stimuli trigger the appearance of neurotransmitters in neurons that normally produce different ones. Many of studies of these processes have been carried out in cell culture, providing important insights into the capabilities of developing neurons. Ultimately, however, we want to understand how differentiation proceeds in vivo. The proposed research has three specific aims, focused on understanding these processes in the intact nervous system of larvae of the frog, Xenopus laevis, which facilitates behavioral, cellular and molecular analysis. The immediate goal of this research is to test the hypothesis that activation of a neural circuit by a natural olfactory stimulus leads to transmitter respecification in neurons in the circuit with corresponding changes in behavior controlled by the activated circuit, and that specific molecular mechanisms are involved. The long- term goal of this research is to understand how neural network activation can be used to induce neurotransmitter plasticity in the brain.